New data from the Cassini spacecraft suggest that the shape of our solar system moving through the local Milky Way galaxy looks like a bubble -- or a rat -- traveling through a boa constrictor’s belly. The boa’s ribs mimic the local interstellar magnetic field, expanding and contracting as the rat passes. For decades, scientists believed our solar system looked more like a comet as it moved through the interstellar medium. (See that old image here.)

Previous models of the boundary region between the heliosphere and interstellar medium have been based on the assumption that the relative flow of the interstellar medium and its collision with the solar wind dominate the interaction. This would create a foreshortened "nose" in the direction of the solar system's motion, and an elongated "tail" in the opposite direction.

However, the Cassini/MIMI/INCA data show a belt of hot particles, consistent with heated particles confined by the interstellar magnetic field. As it zooms away from the sun, the video shows an artist's concept of the interstellar medium flowing past the heliosphere, with the interstellar magnetic field parting and sliding around the bubble of hot, high pressure particles and containing those particles in a more spherical configuration. The measurements of this belt will provide valuable constraints on refined models of the heliosphere and its interaction with the interstellar medium.